diff --git a/src/device/hwm_gl518sm.c b/src/device/hwm_gl518sm.c
index 4afe016f2..102026294 100644
--- a/src/device/hwm_gl518sm.c
+++ b/src/device/hwm_gl518sm.c
@@ -31,8 +31,7 @@
 
 #define CLAMP(a, min, max)		(((a) < (min)) ? (min) : (((a) > (max)) ? (max) : (a)))
 /* Formulas and factors derived from Linux's gl518sm.c driver. */
-#define GL518SM_RPMDIV(r, d)		(CLAMP((r), 1, 960000) * (d))
-#define GL518SM_RPM_TO_REG(r, d)	((r) ? CLAMP((480000 + GL518SM_RPMDIV(r, d) / 2) / GL518SM_RPMDIV(r, d), 1, 255) : 0)
+#define GL518SM_RPM_TO_REG(r, d)	((r) ? CLAMP((480000 + (r) * (d) / 2) / (r) * (d), 1, 255) : 0)
 #define GL518SM_VOLTAGE_TO_REG(v)	((uint8_t) round((v) / 19.0))
 #define GL518SM_VDD_TO_REG(v)		((uint8_t) (((v) * 4) / 95.0))
 
diff --git a/src/include/86box/86box.h b/src/include/86box/86box.h
index 110a9d3d4..8b84100fd 100644
--- a/src/include/86box/86box.h
+++ b/src/include/86box/86box.h
@@ -42,6 +42,9 @@
 #ifdef MAX
 #undef MAX
 #endif
+#ifdef ABS
+#undef ABS
+#endif
 
 #define MIN(a, b)	((a) < (b) ? (a) : (b))
 #define MAX(a, b)	((a) > (b) ? (a) : (b))